The present invention relates to a permanent current switch that switches a superconducting coil operating under conduction cooling between a permanent current state and a power supply connection state in a superconducting magnet device or a magnetic resonance imaging apparatus using that magnet device.
As the background art in the present technical field, there is a publication, Japanese Unexamined Patent Application Publication Hei8-138928. In this publication, there is disclosed a technique for making a superconducting coil stable thermally and decreasing heater capacity with heating means for heating the superconducting coil of a permanent current switch and a thermal switch for thermally shirt-circuiting and decoupling the permanent current switch part to/from a cooling stage cooled with a cooling source. In Japanese Unexamined Patent Application Publication No. 2003-142744, a technique is found that obtains the function and operation of a thermal switch in a permanent current switch that is cooled via a thermal switch heat transfer plate by using a material having a large thermal conductivity at a temperature of 20 K and a small coefficient of thermal conductivity at 100 K for the material of the thermal switch heat transfer plate.